Wound dressing

ABSTRACT

A wound dressing including at least one skin adherent facing layer comprising a discrete layer of silicone gel having a plurality of preformed apertures arranged in a pattern. The pattern of apertures may be equally spaced and generally uniform in shape. The wound dressing may include a facing layer with at least two discrete, adjacent silicone gel layers having different strength properties.

This application claims the benefit of U.S. Provisional Application Nos.60/437,146 filed 31 Dec. 2002, 60/482,775 filed 27 Jun. 2003, 60/503,546filed 17 Sep. 2003, and 60/518,317 filed 10 Nov. 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wound dressing, and more particularlyto a wound dressing having a construction with improved skin adherenceand absorptive capabilities, and methods for producing the same.

2. Discussion of Related Art

Historically, many diverse materials of various origins have been usedto treat wounds by absorbing wound fluids and tissue, hereinaftergenerally referred to as exudate, from a wound site with some type ofabsorbent material. In recent years, use of polymeric-based wound careproducts have become increasingly popular to control wound siteenvironmental factors such as water vapor, oxygen permeability,bacterial impermeability, and absorption of exudate. Such wound careproducts are tailored to meet specific requirements includingconformability to a body portion, selective adherence to a wound bed,and adhesiveness to the skin surrounding the wound site.

Recently, occlusive or moisture-retentive dressings have gainedincreasing acceptance in treating wounds, in particular pressure soresand ulcers. A wide variety of types of structures are known in the artfor use in or as occlusive dressings and generally comprise componentsfor receiving, absorbing and retaining exudate. Typically, these woundcare products include polymeric foams, polymeric films, particulate andfibrous polymers, hydrogels and hydrocolloids. Dressings with at leastone of these components promote wound healing by providing a moistenvironment, while removing excess exudate and toxic components, andfurther serve as a barrier to protect the wound from secondary bacterialinfection. While these known occlusive wound dressings can effectivelymanage a wound, many have been found to possess certain limitations ordisadvantages.

In wound care, one of the main objectives of a wound dressing is toincrease, improve or maximize utilization of the absorbent capacity ofthe dressing so as reduce or eliminate maceration, and facilitate thehealing process of the wound. The control of exudate is of primeimportance if a moist wound microenvironment is to be maintained.Unfortunately, many wound dressings have been found to remove all theexudate that a wound produces, thereby causing a “dry” wound that isundesirable in the wound healing process or in the alternative, suchwound dressings have been found to absorb or control the exudateinsufficiently, thereby leading to a pooling of the exudate which mayincrease the risk of bacterial proliferation and lead to infection.

Many wound dressings in the prior art include an absorbent layer havingabsorptive capabilities. Typically, the absorbent layer containshydrophilic materials that absorb exudate and permit the wound dressingto be left in place for a period of days. Such absorbent layers maycomprise a non-woven material or foam containing hydrocolloid particlessuch as the dressings described in U.S. Pat. Nos. 4,373,519 and6,566,576, or a hydrophilic foam layer, such as in the dressingsdescribed in U.S. Pat. Nos. 5,409,472, 5,782,787, 6,040,492, 6,051,747,and 6,486,378.

While absorbent layer dressings are configured to absorb wound exudate,they often possess the disadvantage of being limited in the amount ofexudate that may be absorbed. The limit to the maximum absorption ofabsorbent foam is often directly related to their geometrical size priorto absorbing a fluid. For example, hydrophilic foams may expand only to12-15% of their original size. Another disadvantage is that it has beenfound that a certain amount of the exudate can be “squeezed” out ofabsorbent foam dressings due to poor liquid retention. The ability ofexudates to be squeezed from the foam layer, and thus dressing itself,poses a risk of infection and may interfere with the healing of thewound.

Yet another disadvantage with known dressings is that absorption ofexudate by an absorptive layer in contact with the wound causes thecentral portion of the applied dressing to swell and push up against thewound. Continued swelling can induce separation of the skin adherentlayer from the skin outside the wound area, especially at the border ofthe wound dressing whereat a “curling” effect may occur. This excessiveswelling of the wound dressing may further lead to leakage of theexudate from the periphery of the dressing, thereby providing a tractfor the invasion of pathogenic microorganisms and further promotingmaceration of the wound site.

Conventionally, a backing layer is provided that comprises a liquidimpervious film that is attached to the absorbent layer to preventexudate from seeping from the dressing. A difficulty arises during fluiduptake in that as the absorbent core expands, the backing layer mustaccommodate the expansion of the absorbent layer without causing curlingof the dressing. An attempted solution to this problem is described inU.S. Pat. No. 4,738,257 which discloses a backing layer formed of a thinelastic sheet which is yieldable as the absorbent core swells. It hasbeen found, however, that a liquid impervious plastic film cannot bemade to sufficiently stretch in keeping with the expansion of theabsorbent layer, and as a result, the film counteracting with theswelling absorbent layer may produce the aforesaid curling at the borderof the dressing. Another proposed solution is provided in U.S. Pat. No.6,040,492 which discloses a wound dressing that includes a backing layerthat is attached to an absorbent foam core and includes a plurality ofwrinkles that substantially flatten as the foam core swells. While thebacking layer may accommodate the expansion of the foam core, the fluiduptake of this wound dressing is limited by the expandability of thefoam core itself. Accordingly, due to the limited absorptive capacity ofthe foam core, the dressing must be replaced often.

Ideally, a wound dressing must be adhesive in nature such that it mayattach to the wound site while being non-toxic and eliciting no morethan a minimal allergenic response. Moreover, a wound dressing shouldpossess the ability to prevent bacteria from entering the wound from theambient environment while providing a suitable moisture transmissionrate.

It has been found, however, that many known occlusive dressings possessthe disadvantage of relying solely on a pressure sensitive adhesivelayer that is used to secure the dressing to skin, for instance anacrylate glue having a high specific adhesiveness. Typically, a wounddressing with only an adhesive has a tendency to strip the centralportion of the dressing from the wound when removed from the wound andthus may damage healing tissue.

Wound dressing have been commercially available that include anabsorbent foam core with a wound contacting surface coated with a layerof silicone gel. The silicone gel randomly lines portions of the wallsof the pores of the absorbent foam to form a plurality of randomlyformed apertures. These apertures are formed by capillary action when anuncured silicone gel is applied to the foam core. One drawback to thisapproach is that the silicone gel may close some of the pores, andanother drawback is that the holes are randomly formed which may lead tolocalized areas that inhibit the uptake of the exudate into the foamcore. While in some applications it may be desirable to provide thewound dressing with a greater concentration of apertures at selectedregions of the wound dressing to increase exudate uptake at such areas,this approach does not accommodate such a formation of a predeterminedpattern of apertures. Furthermore, another drawback to this approach isthat the surface roughness of the silicone layer is largely dependentupon the surface of the foam to be coated, and in the event it isdesired to obtain a smooth silicone layer to be worn on the skin, thisapproach fails to yield such a smooth silicone layer.

Developments in the field of silicone manufacturing have led Ossur hf ofReykjavik, Iceland, and assignee of the present invention, to producesilicone products adapted for skin contact that provide superb softness,gentle skin contact, and may include unique skin care ingredients. Inparticular, such silicone manufacturing has led to advances in improvedcomfort and cushioning of prosthetic suspension liners that haveexcellent durability and intimacy using proprietary silicone technologyof Ossur hf. It has been found that by applying the silicone technologyof Ossur hf to produce an ultra-thin, perforated tacky silicone sheet, asilicone adhesive layer can be produced that possesses superior gentleadherence to wound sites while not damaging skin and the wound bed dueto single or repeated removal of the silicone layer.

Despite the availability of a variety of absorbent wound dressings,there is a need and a demand for an improved wound dressing whichprevents wound trauma upon wound dressing changes, improves thedurability and lifetime of the wound dressing, anatomically conforms toa wound and possesses improved fluid uptake, retention and removalproperties. Most importantly, it is desired to produce a wound dressinghaving an adhesive layer that does not possess the drawbacks of knownadhesive layers, and instead, gently adheres and detaches from a woundsite while providing superior fluid uptake. Moreover, there is a needand a demand for an improved method of forming such an improved wounddressing that is both simple and cost effective.

SUMMARY OF THE INVENTION

The present invention is directed to an improved wound dressingpossessing superior absorbent capabilities including increased fluiduptake and enhanced retention properties. In an embodiment of theinvention, a wound dressing includes a skin adherent facing layercomprising a discrete layer of silicone gel having a plurality ofpreformed apertures arranged in a pattern. In another embodiment of theinvention, the wound dressing includes a skin adherent facing layerhaving a discrete layer of silicone gel including a plurality ofpreformed apertures arranged in a pattern. In yet another embodiment,the facing layer includes at least two different discrete layers ofsilicone gel.

Embodiments of the invention include various configurations of thepattern of the apertures, such as patterns wherein the apertures havedifferent shapes, densities along varying regions of the facing layer,alternating sizes, and different spacing arrangements.

The skin adherent, facing layer employs the silicone technology andknow-how of Ossur hf. The silicone gel layer has properties that permitthe gel to adhere gently to surrounding skin at the wound site. Thesilicone gel layer is inherently soft to the touch and flows partly intomicroscopic cavities and cracks in the skin when applied thereon tocreate a large contact area over the wound site.

Numerous other advantages and features of the present invention willbecome more readily apparent from the following detailed description ofthe invention, the accompanying examples, drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a wound dressing of theinvention;

FIG. 2 is a sectional view of the wound dressing along line 11-11 inFIG. 1;

FIG. 3 is a perspective view of an embodiment of a wound dressing of theinvention;

FIG. 4 is a plan view showing an embodiment of a facing layer of theinvention;

FIG. 5 is an enlarged view of a section of another embodiment of thewound dressing in FIG. 2;

FIGS. 6-8 are sectional views illustrating progressive swelling of thewound dressing in FIGS. 1-2 over a wound site;

FIG. 9 is an enlarged view of a section of the wound dressing in FIG. 8;

FIG. 10 is a plan view showing an embodiment of a facing layer of theinvention;

FIG. 11 is a plan view showing an embodiment of receptacles of anabsorbent core of the invention;

FIG. 12 is a plan view showing an embodiment of a facing layer of theinvention;

FIG. 13 is an elevational view showing another embodiment of receptaclesand a facing layer of the invention;

FIGS. 14-16 are plan views showing embodiments of facing layers havingregions with different degrees of skin adherence of the invention;

FIGS. 17-18 are elevational views showing embodiments of a backing layerhaving a skin adherent border section of the invention;

FIG. 19 is a perspective view of an embodiment of a perforation platefor forming apertures in a facing layer of the invention;

FIG. 20 is an elevational view showing the perforation plate of FIG. 19;

FIGS. 21-23 are schematic views showing arrangements for formingapertures in facing layers of the invention;

FIG. 24 is a perspective view of an arrangement for forming apertures inthe facing layer of the wound dressing of FIG. 23;

FIGS. 25-26 are schematic views showing an arrangement for formingreceptacles in an absorbent core of the invention;

FIGS. 27-28 are schematic views showing an arrangement for depositingdiscrete portions of absorbent material in receptacles of an absorbentcore of the invention;

FIG. 29 is a cross-sectional view showing an embodiment of a platen usedto apply a backing layer to an absorbent core of the invention; and

FIGS. 30-34 are schematic views showing an arrangement for applying abacking layer to an absorbent core of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIGS. 1 and 2, the wound dressing 10 of the presentinvention preferably includes a perforated hydrophobic, skin adherentfacing layer 12, an absorbent core 14, and a liquid impervious, moisturepermeable backing layer 16. The wound dressing depicted in FIG. 1 is ina dry state substantially devoid of moisture. As more fully exemplifiedin FIG. 2, the absorbent core 14 defines a proximal surface p that isintended to face towards a wound surface and a distal surface d that isopposed to the proximal surface p and faces away from a wound surface.In a basic configuration, the dressing 10 comprises the facing layer 12secured to the proximal surface p of the absorbent core 14 and thebacking layer 16 attached and sealed to at least part of the distalsurface d of the absorbent core 14.

In a preferred embodiment, the absorbent core 14 defines a plurality ofreceptacles 18 arranged in a predetermined pattern wherein thereceptacles 18 are defined as a repeating series of cylindricalcompartments. As shown in FIG. 2, the receptacles 18 open at the distalsurface d of the absorbent core 14 and extend a distance into theabsorbent core 14 a distance t₁, short of its entire thickness t. Thereceptacles may assume a variety of configurations and may becylindrical in shape, extend transversely along at least a portion ofthe distal surface of the absorbent core, or assume other possibleconfigurations as will be discussed below. The plurality of receptacles18 contain discrete portions of absorbent material 20 that absorbexudate from the wound and migrate from the receptacles 18 towards thebacking layer 16 upon absorption of such exudate.

As illustrated in FIG. 2, the absorbent core 14 generally definescentral, intermediate and border portions 22, 23, 24. Preferably, thebacking layer 16 is secured to the border portion 24 of the absorbentcore 14 and sealed along its periphery. The border portion 24 preferablyincludes a bevel 28 defined near or along a peripheral edge thereof andis provided to retain any loose absorbent material 20 from thereceptacles 18 within the dressing 10. As will be discussed more fullybelow, the backing layer 16 is preferably lightly adhered to the centralportion 22 of the absorbent core 14 when the dressing 10 is in a drystate.

The backing layer 16 of the dressing 10 preferably includes a compliantelement 26 that is interposed between the central and border portions22, 24 of the absorbent core 14. The compliant element 26 is generallyconcentric with the central portion 22 and comprises a portion of thebacking layer 16 that may not be adhered to the absorbent core 14 whenthe dressing 10 is in a dry state. Preferably, the compliant element 26includes at least one concentric ridge. While FIG. 2 shows the dressing10 with a compliant element 26 having only one concentric ridge 30. FIG.3 illustrates a dressing 10 having a plurality of ridges wherein innerand outer ridges 31, 32 extend outwardly from the distal surface d ofthe absorbent core 14, and generally constitute inner and outerboundaries of the compliant element 26.

It will be understood that the compliant element may assume a varietyconfigurations. For example, the orientation of the compliant elementmay be arranged in a variety of directions such as the ridge extendingin a range of directions from being generally parallel to the absorbentcore on the border portion side of the compliant element to beinggenerally parallel to the absorbent core on the central portion side ofthe compliant element.

As shown schematically in FIG. 5, the compliant element 26 is notlimited to being positioned generally along the intermediate portion ofthe absorbent core. The compliant element 26 may be positioned on theborder or the central portions of the wound dressing wherein thecompliant element 26 may include at least one ridge 30 or segmentthereof on at least one of the border or central portions of the wounddressing. Such adaptation of the wound dressing to include a compliantelement on at least one of the border or central portions of the wounddressing may be provided to improve the expandability and distension ofthe backing layer relative to the distal surface of the absorbent core.

The facing layer 12 is preferably secured to the proximal surface p ofthe absorbent core 14. The facing layer 12 includes a plurality ofapertures 34 that are preformed in a pattern prior to securing thefacing layer 12 to the absorbent core 14. As shown schematically inFIGS. 2 and 4, the plurality of apertures 34 may be arranged in apredetermined pattern. The plurality of apertures 34 may be configuredto correspond to regions near or at the plurality of receptacles 18 ofthe absorbent core 14 so as to transport exudate from a wound site tothe absorbent core 14. The facing layer 12 is preferably secured only tothe proximal surface p of the absorbent core 14 and preferably does notcoat the walls of the pores or holes of the absorbent core 14 definednear the proximal surface p thereof. It will be understood, however,that portions of the facing layer may fill irregularities disposed alongthe proximal surface of the absorbent core or pores of the absorbentcore so as to improve the security of the facing layer to the absorbentcore.

While not wishing to be bound by a particular mechanism of operation,the present invention is intended to function as a dressing 10 in themanner depicted in FIGS. 6 to 8, after application of the dressing to afluid-exuding skin wound. It will be understood that in the context ofthe invention, the terms fluid, moisture and exudate are usedinterchangeably regarding wounds and wound dressings. The dressing 10 isplaced onto a wound site w with the facing layer 12 directed over thewound bed b. The facing layer 12 may adhere to the intact skin aroundthe wound site w as well as to the wound bed b. The dressing 10 ismaintained in close apposition to the wound bed b in part by thecapillary action of the exudate entering the absorbent core 14 and bythe facing layer 12.

As illustrated in FIG. 6, fluid exuded by the wound bed b will be drawnthrough the apertures 34 towards the absorbent core 14, and theabsorbent material 20 contained in the receptacles 18. After beingapplied over the wound site w for an extended period of time, theapplied dressing 10 may appear as shown in FIG. 7 with a slightlyenlarged domed, reservoir configuration 36 extending over the centralportion of the absorbent core 14. The reservoir 36 is caused by theabsorbent material 20 that has absorbed a desired quantity of exudatefrom the receptacles 18 and discrete portions thereof have swelled andmigrated from the receptacles, thereby causing distension of the backinglayer 16. The swollen exudate-laden discrete portions of absorbentmaterial 20 cause the backing layer 16 to detach from the distal surfaced of the absorbent core 14 in a predictable manner and to distendupwardly to further permit continued absorbing and swelling of thedressing 10 over the wound site w. In addition, the absorbent core 14will expand or swell both transversely and longitudinally, and the areaof absorbent core 14 will generally increase with increased fluidabsorption.

While the backing layer 16 remains sealed along the border portion ofthe dressing 10, the reservoir 36 is formed such that it is definedbetween the backing layer 16 and the distal surface d of the absorbentcore 14, and sealed along the border portion 24. The reservoir 36permits the migration of the swollen discrete portions of absorbentmaterial 20 from the receptacles 18 and greatly expands the retention offluid from the wound bed b. The compliant element 26 effectivelyfunctions as a flexible joint for the backing layer 16 by permittingadditional expansion of the backing layer 16 in providing additionalflexibility and expansion of the backing layer 16 due to the swelling ofthe absorbent material 20. As shown in FIG. 8, the dressing 10 hasnearly reached its swelling capacity and the backing layer 16 hasdistended to its maximum. Most notably, at this advance stage ofswelling, the border portion 24 of the dressing 10 remains attached tothe wound site w due to the provision of the compliant element 26 whichcompensates for the expansion and swelling of the absorbent core 14 andthe absorbent material 20, and the distension of the backing layer 16.It will be further noted that the ridge 30 generally does not fullyflatten relative to adjacent portions of the backing layer 16 andgenerally extends outwardly, at least in part, from the distal surface dof the absorbent core 14 and in relation to the distended portion of thebacking layer 16 delimited by the compliant element 26.

It will be understood that the preferred facing layer 12 also hassuitable elastic properties to enable it to stretch as the absorbentcore 14 expands laterally.

When the dressing 10 has expanded to a maximum capacity, defined as anexudate-laden or fully saturated dressing, it will be desirable toremove and replace the dressing 10. When in a saturated or fullyexudate-laden stage, the corners along the border portion 24 of thedressing 10 generally remain adhered to the wound site w despite theexcessive uptake of exudate, as exemplified in FIG. 9, since the facinglayer 12 provides sufficient adherence to the skin surrounding the woundsite w. By observing the extent of swelling of the dressing in relationto the degree of fluid uptake into the absorbent core and by theabsorbent material, one can be visually determine when it is appropriateto remove the dressing.

As exemplified in FIG. 10, the dressing 10 may include an additionaladhesive 19 disposed on the facing layer 12. Preferably, the adhesive 19is deposited on the facing layer 12 at or near a portion correspondingto the border portion of the absorbent core 14. The pressure sensitiveadhesive 19 is preferably a tacky pressure sensitive silicone or anacrylate adhesive known in the art of wound dressings.

In a preferred embodiment, the absorbent core 14 comprises preferably ahydrophilic synthetic polymer conformable to body surfaces and adaptedto be capable of absorbing fluid. It is desirable that the absorbentcore absorb exudate rapidly so as to enhance its effectiveness in thedressing of the invention, and in particular, the fluid uptake to thereceptacles containing the absorbent material. In addition toabsorption, an effective wicking mechanism is desirable, that is theabsorbent core should rapidly direct fluids away from the proximalsurface of the absorbent core to more remote areas for storage (i.e.,the receptacles containing the discrete portions of absorbent material),so as to minimize local saturation and maximize the efficiency of theabsorbent core.

In an exemplary embodiment, FIG. 12 shows how the facing layer 12 may beconfigured to have different sized apertures 34, 86. According to thisembodiment, the apertures are arranged in rows wherein the largeapertures 86 alternate with the smaller apertures 34.

A preferable absorbent core is constructed of flexible open-cell foamthat is at least slightly hydrophilic. Suitable foams have an open cellsize of 30 to 700 microns, and preferably a cell size of 50 to 300microns. The open cells permit transport of fluid and cellular debrisinto and within the foam, and it preferred that the cell size of areasof the foam be of sufficient size to encourage capillary action andpromote fluid transport.

The absorbent core may expand about 135% of its size when saturated withfluid. When combined with the facing and backing layer of the invention,the absorbent core may expand to only about 110% of its dry size whenexudate laden.

In accordance with one embodiment of the invention, the absorbent foamcomprises a gradient of cell sizes across the thickness of the absorbentcore such that the cell size decreases in the direction of the distalsurface and of the absorbent core. Since the cell sizes are greater atand near the proximal surface of the absorbent core, the capillaryforces are stronger and therefore will drain fluid near the proximalsurface of the absorbent core and draw the fluid towards thereceptacles. In addition, the absorbent foam may include a cell sizegradient that is directed towards the receptacles, thereby providinglocalized regions in the absorbent foam that are configured to haveincreased capillary forces directed towards the receptacles to aid inthe guidance of fluid thereto.

The foam may be made, for example, from polyurethane, cellulose,carboxylated butadiene-styrene rubber, polyester foams, hydrophilicepoxy foams or polyacrylate. In a preferred embodiment, the foam isformed from hydrophilic polyurethane foam, such as polyurethane foammade by Reynel Inc. (Boothbay, Me.) under product designation L00562-B.Since the aforesaid foams are hydrophilic per se and further in view ofthe use of the receptacles containing absorbent material, it is notnecessary to treat the foams to render them more hydrophilic in apreferred embodiment.

In another embodiment, if desired, the foam may be treated so as to bemore hydrophilic and therefore increase the tendency of the exudate tocoagulate more rapidly in the foam, yet only to the extent that the foamis not too hydrophilic so that the hydrophilic properties of the foamprevents transport of the exudate to the absorbent material. In such anembodiment, the level of hydrophilic properties of the absorbent foammay be designed such that the surface tension is minimized to allow theeasy passage of fluid into foam cells. The fluid is thus retained in theabsorbent foam while maintaining a high relative humidity at the woundsite.

It will be understood that the absorbent core is not limited to beingconstituted of foam. In another embodiment, the absorbent core may be aporous woven or non-woven material that may be produced by any number ofmeans using known materials available to those skilled in the art. Forexample, the absorbent core may exist as a bulky, loosely formed webcomposed of very short cellulose fibers arranged in a random ornon-random array, a pad of cellulose flakes, chitosan flakes, or apolymeric fibril matrix.

The thickness of the absorbent core will range from 0.5 mm to 20 mm, andis preferably between 3 mm to 5 mm.

The absorbent core may include an array of receptacles formed thereinand may be defined in any suitable preselected pattern that can containa desired bulk or quantity of discrete portions absorbent material,while maintaining sufficient strength and flexibility suitable for adressing of the invention. In a preferred embodiment shown in FIG. 1,the pattern of the receptacles 18 is in a grid-like configuration.Preferably, such receptacles have a uniform, predetermined shape andsize, and extend across the distal surface d of the absorbent core. Inthis embodiment, the receptacles are positioned in a rectangularpattern, and the receptacles are generally spaced apart 5 mm (measuredfrom the center axis of each receptacle). The depth of each receptacleis generally 4-5 mm, and positioned at least 0.5 mm from the facinglayer. In this embodiment, the pattern may be tailored to include morereceptacles at specific regions of the dressing as opposed to otherregions.

In an embodiment of the wound dressing shown in FIG. 11, there is ahigher density of receptacles 18 at the central portion 22 of theabsorbent core 14 than near the border portion 24 of the dressing 10.The amount of receptacles at any given region of the absorbent core maybe dependent upon the perceived areas of a greater amount of localoccurrence of fluid, such as at the central portion, to maximize fluidabsorption, and further limit the absorption of fluid at certain areasof the absorbent core such as at the border portion.

As shown in FIG. 2, the receptacles 18 are arranged to open at thedistal surface of the absorbent core 14 and extend a distance into theentire thickness thereof. In a preferred embodiment, the receptaclesextend a distance t₁, short of the entire thickness t of the absorbentcore 18, and it is preferred that the receptacles extend a distance70-90% of the total thickness of the absorbent core 14. It will beunderstood, however, that in an embodiment of the wound dressing, thereceptacles may extend through the entire thickness of the absorbentcore.

In another embodiment of the wound dressing, the receptacles 18 may bearranged, as shown in FIG. 13, to extend at different distances into thethickness of the absorbent core 14 on the basis of their location andthe local occurrence of fluid exuded from a wound site. In thisembodiment, the receptacles 18 located closer to the center of thedressing 10 extend deeper into the thickness of the absorbent core 14whereas the receptacles 18 closer to the border 24 of the absorbent coreextend a shallower distance into the thickness of the absorbent core 14than the receptacles 18 at the central portion 22. It follows that thedeeper receptacles 18 will contain more absorbent material 20 than theshallower receptacles 18, and therefore provide a greater localizedregion of absorption.

Since the receptacles preferably extend only partly into the totalthickness of the absorbent core, exudate will be transported to andabsorbed by the absorbent material. This effect leaves the proximal sideof the absorbent core without the receptacles in a desirably moistenvironment without excessive saturation of exudate and thus permits thedressing to remain on the wound site for a longer period of time.

In a preferred embodiment shown in FIGS. 1 and 2, the shape of theindividual receptacles 18 is uniform and generally cylindrical. Theshape of the receptacles is at least partly chosen to maximize thecontainment of the discrete portions of absorbent material and tofacilitate the migration thereof when swollen by fluid. The receptaclesare not limited to a cylindrical configuration; the receptacles may takeon the shape of pyramids, channels, hemispheres, cones, blocks andtruncated variations and combinations thereof. Moreover, the receptaclesmay include a taper extending from their opening to their base portionso that the receptacles have a greater width near the opening than atthe base portion. This configuration facilitates migration of swollen,moisture-laden discrete portions of absorbent material from thereceptacles so that they can flow more freely from the receptacles.Alternatively, the receptacles may be arranged in a random pattern alonga transverse direction of the distal surface of the dressing.

In an embodiment of the absorbent core, the receptacles may comprise aplurality of channels extending transversely along at least a portion ofthe distal side of the absorbent core. In this embodiment, the channelsmay have a denticulate or an undulating cross-sectional profile. Thisembodiment may be useful in a wound dressing wherein the absorbent coreis too thin to include receptacles having a form such as the aforesaidcylindrical receptacles.

The size of the individual receptacles may be of any suitable size thatwill contain a suitable amount of absorbent material that willsufficiently absorb exudate from a wound site. Generally, thereceptacles are sized from about 500 to 5,000 micrometers, preferablyabout 1000-3000 micrometers in cross-section (independently height andwidth dimensions). The receptacles in a preferred pattern have a repeatdistance defined as the distance from one receptacle to the nextreceptacle, center axis to center axis, of 500 to 5,000 micrometers,preferably about 1000-4500 micrometers.

While in a preferred embodiment the receptacles have a uniform volumeacross the transverse directions of the wound dressing, the receptaclesmay have varying volumes depending upon the location of their openingson the distal surface of the absorbent core. As with the embodimentrelated to the varying depths of the receptacles, the receptacleslocated at or near the central portion of the absorbent core may havegreater volumetric capacity than the receptacles closer to the borderportion of the absorbent core. It follows that the receptacles havingvarying volumes will likewise contain varying bulk amounts of discreteportions of absorbent material.

The absorbent material used in the dressing of the present invention ispreferably comprised of superabsorbent polymeric granulates, flakes orpowders that swell on exposure to water and form a hydrated gel(hydrogel) by absorbing large amounts of water. Superabsorbents aredefined herein as materials that exhibit the ability to absorb largequantities of liquid, i.e., in excess of 10 to 15 parts of liquid perpart thereof. These superabsorbent materials generally fall into threeclasses, namely starch graft copolymers, cross-linkedcarboxymethylcellulose derivatives and modified hydrophilicpolyacrylates. Examples of such absorbent polymers are hydrolyzedstarch-acrylonitrile graft copolymer, a neutralized starch-acrylic acidgraft copolymer, a saponified acrylic acid ester-vinyl acetatecopolymer, a hydrolyzed acrylonitrile copolymer or acrylamide copolymer,a modified cross-linked polyvinyl alcohol, a neutralizedself-crosslinking polyacrylic acid, a crosslinked polyacrylate salt,carboxylated cellulose, and a neutralized crosslinked isobutylene-maleicanhydride copolymer. Superabsorbent particulate hydrophilic polymersalso are described in detail in U.S. Pat. No. 4,102,340. That patentdiscloses absorbent materials such as cross-linked polyacrylamides.Preferably, the super absorbent particles used in the dressing of thepresent invention are preferably composed of cross-linkedpolyacrylic-acid.

Superabsorbent particles are available commercially, for example starchgraft polyacrylate hydrogel powders are available from Hoechst-Celaneseof Portsmouth, Va. Other superabsorbent particles are marketed under thetrademarks SANWET (supplied by Sanyo Kasei Kogyo Kabushiki Kaisha),SUMIKA GEL (supplied by Sumitomo Kagaku Kabushiki Kaisha and which isemulsion polymerized and spherical as opposed to solution polymerizedground particles), and FAVOR (produced by Degussa AG, Dusseldorf,Germany).

The super absorbent particles are preferably in the form of granules orflakes to provide a greater available surface area hydrocolloid. Thesize of the super absorbent particles is typically within the range of 1to 1000 micrometers when dry. Preferably, the particle size range of theabsorbent particles is 100 to 900 micrometers. The particles which areinsoluble in a wound environment have an absorptive capacity greaterthan 0.5 of water per gram of dry particles.

In another embodiment, the absorbent material may be a hydrophilic gelthat swells upon contact with water. The hydrophilic gel generally lacksa cellular or voided internal structure, and is in the form of a solidor semi-solid. Hydrophilic gel may be construed to mean hydrocolloids,hydrogels and combinations thereof as long as the material isphysiologically tolerable and clinically acceptable. A description ofsuitable hydrophilic gels is provided in U.S. Pat. No. 6,566,575 grantedto Stickels et al. and such hydrophilic gels are commercially available.

In another embodiment of the wound dressing, the absorbent core mayinclude a plurality of discrete portions of absorbent material enmeshedin the absorbent core. Such discrete portions of absorbent material maybe discrete superabsorbent polymeric granulates, flakes or powders thatare freely disposed in the absorbent core so that they may migratewithin the absorbent core, and preferably towards the distal surfacethereof. In yet another embodiment of the wound dressing, the absorbentcore may include both absorbent material enmeshed therein and thereceptacles containing discrete portions of the absorbent material.

In summary, in each of the absorbent core embodiments discussed thusfar, it is notable that the absorption of the fluid at the portion ofthe absorbent core near or at its proximal portion is minimized, and theabsorption of fluid is maximized by the absorption of the absorbentmaterial at or beyond the receptacles. Such a mechanism maximizes theamount of fluid that the dressing can absorb, in combination with theconfiguration of the backing layer, and further allows longer wear timefor the patient since the fluid is not in contact with the skin.

A backing layer may be present in all of the embodiments of the dressingof the present invention. Preferably the backing layer is conformable toanimal (inclusive of human) anatomical surfaces, is impermeable toliquid and is vapor permeable. As discussed above, the backing layer, incombination with the absorbent core, may be constructed to define areservoir therebetween when the dressing is in an expandedmoisture-laden state. While the backing layer does not permit thepassage of a liquid or exudate, moisture in the absorbed exudate passesthrough the backing layer in a vapor form into the atmosphere.

The preferred embodiment for the backing layer is a thin polymericelastic or flexible film coating providing a bacterial barrier formedfrom a water vapor permeable pliable elastomer material. The film iscontinuous in that it has no perforations or pores which extend throughthe thickness of the film. Films of this type are known and generallyare hydrophilic polymeric materials through which water vapor is capableof diffusing.

The backing layer is bonded to the proximal surface of the absorbentcore, and in a preferred embodiment, the backing layer is bonded only tothe distal surface of the absorbent core and does not penetrate anypores, cells or cavities therein. Generally, the film is 15 to 45micrometers in thickness, with a preferred thickness of about 30micrometers. The backing layer may comprise polyurethane, such as apolyurethane film available from InteliCoat Technologies (South Hadley,Mass.) under product designation INSPIRE, elastomeric polyester, blendsof polyurethane and polyester, polyvinyl chloride, and polyether-amideblock copolymer. The preferred backing layer for use in the presentinvention is a polyurethane film since it exhibits a resilient propertythat allows the film to have good conformability and further has a highdegree of stretchability.

It is preferred that the backing layer of the present invention be atleast translucent, and more preferably, sufficiently transparent so thatthe wound site to which the dressing is applied can be viewed throughthe dressing. It is advantageous to view to evaluate the wound andhealing thereof without removal of the dressing to avoid unnecessaryhandling of the dressing and exposure of the wound to the environment,which reduces the likelihood of contamination.

Suitable continuous conformable backing layers will have a moisturevapor transmission rate (MVTR) of the backing layer alone of 1500 to14600 g/m^2/24 hrs, preferably 2500 to 2700 g/m^2/24 hrs at 38° C. Thebacking layer thickness is preferably in the range of 10 to 1000micrometers, more preferably 100 to 500 micrometers. The facing layer ofthe present invention is preferably a hydrophobic, liquid and moistureimpervious layer bonded to the proximal surface of the absorbent core.In a preferred embodiment, the facing layer is a cross-linked siliconeelastomer gel, such as, for example, a cross-linked silicone(polydimethyl siloxane gel) manufactured by NuSil Technology(Carpenteria, Calif.) under product designation MED-6340. The facinglayer preferably has a thickness in the range of 0.05 mm to 0.5 mm, andmore preferably 0.1 mm. The conformability of the dressing to the woundis somewhat dependent on thickness of the components, such that when thedressing is applied to a body portion, it conforms to the surface evenwhen the surface is moved. When the surface is flexed and then returnedto an un-flexed position, the facing layer stretches to accommodate theflexation of the joint but is resilient enough to continue to conform tothe surface when the surface is returned to its unflexed condition.

A silicone facing layer has significant advantages over wound dressingsthat rely on a glue-type adhesive to secure a dressing to a wound. Inparticular, tacky silicone gels provide a coating which is exceptionallynon-adherent to wounds, but which is significantly adherent tosurrounding skin. Moreover, such gels are entirely immobile andunaffected by heat or body exudates. This means that dressings accordingto the invention retain their non-adherent properties even after theyhave been in place for a substantial period of time, for example,several days.

The silicone gel layer adheres gently to surrounding skin since it isinherently soft to the touch and flows partly into microscopic cavitiesand cracks in the skin to create a large contact area over the woundsite. As a result, less adhesion force is required to secure thesilicone layer over the wound site than in known dressings that includean adhesive layer having glue. Since the silicone layer more fullydistributes its adhesion force, the peeling strength thereof does notstrip epidermal cells when the dressing is removed from the wound site.Accordingly, the dressing can be reapplied without causing damage to theskin and wound at the wound site. Furthermore, the silicone layerprevents a moisture build-up under such a layer since it is hydrophobicand further since the capillary forces of the absorbent core draw theexudate into the dressing this enables the dressing to be lifted fromthe skin without causing pain to the wearer of the wound dressing.

The silicones which are used as the facing layer in the dressing of theinvention preferably have a Shore A hardness less than 1, and mostpreferable have no measurable Shore A hardness.

When the silicones are formed by cross-linking a mixture of two or moresilicones, the molecular weights of the various components and theirdegree of substitution by reactive groups may be different. This allowsgels having different physical properties to be formed merely by varyingthe proportions of the components.

The composite facing layer also may include one or more skin treatmentagents blended into the silicone elastomer, for example petroleum jellyand aloe vera. In a preferred example, up to 20% by weight of thecomposite elastic layer, preferably 11.9%, may be petroleum jelly, andup to 3%, preferably 0.1%, may be a secondary skin treatment agent suchas aloe vera. It will be understood that different or additional skintreating agents may be utilized, depending upon the skin condition to betreated by the skin treating agent.

In a preferred embodiment, the silicone facing layer is formed as asilicone gel sheet having a predetermined pattern of apertures that areformed prior to the silicone gel sheet being bonded to the absorbentcore. Typically, the apertures will have a diameter of 0.05 to 1.0 mmand there are approximately 50-350 apertures per cm^2. While in apreferred embodiment in FIG. 2 the apertures 34 are shown as generallybeing arranged in a uniform pattern, the facing layer 12 is not limitedto this arrangement.

The silicone facing layer may be substantially planar along a proximalsurface thereof. Moreover, the silicone facing layer may penetrate orfill surface irregularities of an absorbent core defined as openings,crevices or partial pores located along a surface thereof.

In another embodiment exemplified in FIG. 13, there may be a higherdensity of apertures 34 in the facing layer 12 corresponding to thecentral portion 22 of the dressing 10 while there is a lower density orabsence of apertures 34 near or along the border portion of thedressing. Alternatively, the facing layer may entirely lack apertures atthe border portion of the dressing, and more particularly, a regioncorresponding to the beveled portion of the absorbent core. This willmitigate fluid absorption at certain areas of the dressing, thereby moreeffectively directing the exudate absorption in areas that will moreefficiently absorb exudate. Furthermore, in yet another embodiment,there is a greater concentration of apertures at or near portions of theabsorbent core having the receptacles to thereby enhance exudate uptaketowards such receptacles.

Notably, the facing layer is bonded only to the proximal surface of theabsorbent core and may penetrate the absorbent core a distanceapproximately 50% of its thickness. By forming the apertures prior tobonding to the absorbent core, the facing layer does not occlude thecells nor coat the inside walls of the cells of the absorbent core.Accordingly, suitable permeability of the facing layer is preferablyobtained by providing the facing layer with preformed apertures locatedin a suitable array, and accordingly, there is greater control inestablishing the transit of fluid through the silicone gel layer.

The thickness of the facing layer may vary across the length thereof.For example, the facing layer may include regions having greaterthickness near the border portion of the wound dressing as opposed tothe central portion so as to provide greater strength to the facinglayer at such regions thereof having a thicker facing layer.

In yet another embodiment, the facing layer may include at least twodifferent layers having different properties. For example, a softerlayer to be worn directly adjacent the wound site may be provided thatclosely conforms to the wound site while a harder layer may be providedthat this interposed between the softer layer and the absorbent core toprovide durability and strength to the dressing. The multiple layered ormore aptly dual durometer facing layer adopts the principles describedin U.S. Pat. No. 6,136,039 granted Oct. 24, 2000 owned by assignee ofthe invention described herein, the disclosure of which is incorporatedherein.

In another embodiment, the facing layer of the present invention maycomprise a silicone layer of the type mentioned above that is reinforcedwith an embedded perforated reinforcement layer. Such a reinforcementlayer may include a non-woven, knitted or woven textile material, or apoymeric film such as one made of polyurethane. In this embodiment, theapertures in the silicone layer generally correspond to the perforationsof the reinforcement layer.

It will be understood that non-silicone facing layers may be employed inthe dressing of the present invention without departing from the scopethereof. Preferably, such facing layers should be soft, flexible,conformable, non-irritating and non-sensitizing. The dressing mayinclude facing layers that comprise a perforated base film constructedof a variety of polymers such as polyurethane, polyethylene,polypropylene, polyamide or polyester material with a pressure-sensitiveadhesive. Furthermore, the facing layer may be in the form of moisturevapor permeable films, perforated films, woven-, non-woven or knit websor scrims. The adhesive may be a microsphere or fibrous adhesive withlow trauma properties and have good adhesion to wet skin. It will beunderstood that the adhesive may be coated on only a portion of thefacing layer, for example, the adhesive may be applied only around theborder portion of the dressing with the central portion lacking anadhesive. Preferably, the facing layer should be perforated so as topermit transport of the fluid therethrough to the absorbent core.

The dressing the present invention can include various combinations ofingredients without departing from the scope of the present invention,including, for example, medicaments, soaps, disinfecting and sterilizingagents, odor management, hemostatic agents, proteins, enzymes andnucleic acids. Preferably these agents may be incorporated directly ordispersed in the absorbent core, or dispersed with the absorbentmaterial. Alternatively, these ingredients may be incorporated into thedressing by any suitable means, including an additional layer to theabsorbent core that would incorporate such ingredients.

Suitable medicaments, soaps, disinfecting and sterilizing agents,proteins, and enzymes are commercially available. Preferably suchmedicaments may include antifungal agents, antibacterial agents,angiogenesis promoting agents and other appropriate agents.

As mentioned above in observing FIG. 10, the facing layer 12 may includean adhesive that is provided near or at a peripheral border portion ofthe facing layer. Preferably, this adhesive is a pressure sensitivesilicone such as an adhesive silicone manufactured by NuSil Technology(Carpenteria, Calif.) under product designation MED-1356 or a very tackysilicone manufactured by NuSil Technology (Carpenteria, Calif.) underproduct designation MED-6345. The adhesive silicone may applied to asilicone facing layer after the facing layer is cured such that theadhesive silicone is applied to the facing layer when it is in apartially cured state and then finishes curing when on the facing layer.Alternatively, the adhesive may be an acrylate glue or hot melt glueapplied onto the facing layer using conventional methods for applying anadhesive to a substrate.

In a preferred method of the invention, the tacky silicone gel isprepared from a two-component silicone, such as MED-6340 parts A and Bproduced by NuSil Technology (Carpenteria, Calif.). The two parts A andB each include the same base, vinyl-substituted, poly(dimethlysiloxane).In addition, part A includes a platinum catalyst to facilitate areaction between parts A and B when they are mixed. Part B includes across-link, hydride-containing silicone. Both parts A and B are easilymixed, and handled separately, do not react or cure.

The tacky silicone gel is produced by thoroughly mixing parts A and B ina ratio of 1:1, thereby enabling the vinyl-group on thevinyl-substituted silicone to be activated by the catalyst and thehydride containing silicone. This results in cross-linking the siliconeso that it will begin to cure. One of the factors that influences thetime required for curing is the temperature of the mixed combination ofparts A and B. A suitable temperature range is 50-150° C., preferably100-130° C. Another factor that influences the curing time is the amountof catalyst that is used in the combination of parts A and B, howeverthe catalyst may also undesirably influence the tackiness of thesilicone gel. Typically, in the present invention, the curing time of a0.1 mm thick silicone gel facing layer cured at 100° C. is approximately1 minute, and the silicone gel facing layer is normally transferred tothe absorbent core when it is in a partially cured state in a range of3-12 seconds after parts A and B have been mixed.

It will be understood that the aforementioned steps for preparing thetacky silicone gel are provided for exemplary purposes and the inventionis not meant to be limited by such steps. Any suitable steps forpreparing a partially cured tacky facing layer may be used while stillbeing within the scope of the present invention.

In the context of the present invention, “partially cured” siliconedenotes that the silicone is not completely cured and therefore thesilicone is not fully cross-linked. Typically, the parameters foryielding a partially cured silicone layer must be establishedempirically with respect to the gel mixture and absorbent material used.While the parameters for yielding a “partially cured” silicone layer mayvary, the ratio of time required for the silicone gel to become fullycured may be employed to determine if the silicone layer is partiallycured. Specifically, in the present invention, the silicone layer ispartially cured between 5-70% of the total time required to cure thesilicone gel. It follows that the time interval to apply the facinglayer to the absorbent core is between 5-40%, or more preferably 5-20%.

When curing the silicone layer, a catalyzer may be used to speed up thecuring time and reduce the tackiness of the silicone gel. A siliconecatalyzer is commercially available from NuSil Technology (Carpenteria,Calif.) under the product designation CAT-50.

Another preferable feature of the facing layer of the present inventionis a variable tackiness across the surface thereof. According to thisfeature, the tackiness of the facing layer is configured differently atdifferent regions thereof. For example, regions of the facing layer nearor at the border portion of may be provided with a greater tackinessthan the central portion of the facing layer. The tackiness may bedisposed in a gradient across a half section of the facing layer from amaximum at or near the border portion of the facing layer to a minimumat or near the central portion of the facing layer. An embodiment of thewound dressing having a facing layer 12 with variable tackiness isexemplified in FIG. 14. As shown, the facing layer 12 may be provided indiscrete multiple sections having generally uniform tackiness such as aborder portion 33 having greater tackiness than a central portion 37 andan intermediate portion 35 of the facing layer 12. The tackiness maygradually increase from the central portion 37 towards the borderportion 33, or the tackiness may remain relatively constant in eachdiscrete portion 33, 35, 37.

The facing layer is not limited to a border portion having a uniformtackiness. The facing layer may include at least one side of the borderportion having tackiness greater than other portions thereof. Forexample, as exemplified in FIG. 15, if the dressing has a generallysquare or rectangular configuration, two opposing sides 39 correspondingto the border portion of the facing layer 12 may have a greatertackiness than the remaining opposing sides 41 of the facing layer.Alternatively, in the event the dressing has a generally circularconfiguration or variations thereof, as shown in FIG. 16, sections 43 ofthe facing layer 12 corresponding to the border portion thereof may havea greater tackiness than other sections of the border portion of thefacing layer 12.

According to a 90° peel-off test from a stainless steel surface, thetackiness corresponding to the central portion of the silicone facinglayer is generally within the range of 0.05 N - 1.0 N and preferablywithin the range of 0.1 N to 0.4 N. The tackiness corresponding to theborder portion of the silicone facing layer is within the range of 0.5N - 5.0 N and preferably within the range of 0.8 N - 3.0 N.

The facing layer with variable tackiness may be obtained by forming afacing layer wherein areas thereof have different mixtures of siliconecomponents, the presence or different quantities of silicone catalyzeror other components, exposure to different curing conditions such aspressure or temperature, or any other method known to one skilled in theart of obtaining different tackiness in a silicone substrate. Moreover,in the embodiments such as those exemplified in FIGS. 14-16,discontinuous discrete sections of the facing layer having differenttackiness can be prepared and applied to the absorbent core separatelyor the facing layer can be formed with a continuous facing layer havingdiscrete sections of different tackiness.

In another embodiment of the wound dressing exemplified in FIG. 17, thebacking layer 16 may be configured so as to define a border section 45that extends beyond the border of the absorbent core 14 and the facinglayer 12 disposed thereon. The border section 45 of the backing layer 16preferably surrounds the peripheral edges of the absorbent core 14 andthe facing layer 12. The border section 45 of the backing layer 16 maybe provided with a skin adherent adhesive or an elastomeric gel that ispreferably tackier than the facing layer 12. The stronger adhesion ofthe border section 45 of the backing layer 16 permits the dressing 10 toremain firmly in place over a wound site. In this embodiment, the facinglayer 12 preferably has a gentle adhesion that will preventtraumatization of a wound upon removal therefrom.

In yet another embodiment shown in FIG. 18, the backing layer 16 isadhered to the absorbent core 14 such that the absorbent core extendsfrom the backing layer 16. The facing layer 12 is configured to extendaround the sides of the absorbent core 14 and will generally extend tomeet with the backing layer 16. The backing layer 16 includes a bordersection 45 that may have a stronger tackiness than the facing layer 12.

In the embodiments shown in FIGS. 17 and 18, the backing layer may beprovided with or without the aforementioned compliant element and theabsorbent core may be provided with or without the receptaclescontaining discrete portions of absorbent material.

The entirety of the side of the backing layer adjacent the absorbentcore may include the skin adherent adhesive or an elastomeric gel usedfor the border section 45. In a such an embodiment, the skin adherentadhesive or an elastomeric gel, however, is preferably disposed on thebacking layer so that it does not prevent moisture transfertherethrough. In the alternative, the skin adherent adhesive or anelastomeric gel disposed on the border section of the backing layer maybe applied, such as sprayed or spreaded, to the border section of thebacking layer after the backing layer is applied to the absorbent core.

The method of manufacturing this embodiment may be conducted using oneof the methods described herein for applying the backing layer to theabsorbent core. Alternatively, one side of the backing layer may becoated with a discontinuous adhesive or elastomeric gel on a side thatwill face the absorbent core. The backing layer is thus placed onto theabsorbent core so that the backing layer extends over an entire surfacethereof wherein a section of the backing layer extends beyond theperipheral edges of the absorbent core to define the border section.Prior to applying the backing layer to the absorbent core, a primer maybe applied to the side of the absorbent core adjacent to the backinglayer such that the primer is applied discontinuously so that the primerdoes not prevent transport of moisture through the backing layer whenapplied on the absorbent core.

In a preferred method, the facing layer and its apertures are formedprior to being bonded onto the absorbent core. A perforation device 42is preferably used to form the facing layer and its apertures. As shownin FIGS. 19 and 20, the perforation device 42 includes a generallyplanar carrier surface 47 having a plurality of needle-like perforatingelements 44 that extend a distance therefrom. The perforation device 42,including the carrier surface 47 and the perforating elements 44, isselectively heated to a curing temperature of the silicone. The carriersurface 47 and the perforating elements 44 are coated with a releasefilm, such as TEFLON.

In a preferred embodiment, the perforating elements extend a distanceslightly greater than the thickness of the silicone layer, and can varyin length from 0.02 to 1.0 mm with a preferable length of 0.1-0.2 mm.While in this embodiment the perforating elements have a generallycircular cross-section, the pins are not limited to this configuration.For instance, the pins may alternatively have a cross-section configuredin a triangular, square, rectangular or any other suitable shape orcombination thereof. The perforation device has a density of 5 to 300perforating elements per cm^2, and preferably there are 100 perforatingelements per cm^2.

When forming the facing layer, a discrete layer of uncured silicone gelis disposed on the carrier surface of the perforation device such thatthe perforation elements extend through the layer of silicone gel. Theuncured silicone layer generally has a thickness ranging between0.05-0.5 mm. The perforation device is heated to a predeterminedtemperature, about 100° C. or to any other suitable curing temperatureof the silicone gel, either before or after the silicone gel is placedthereon. The silicone gel will begin to cure along an inner side portionthereof that is adjacent to the carrier surface as it is smoothed overthe carrier surface. It will be understood, however, that it is notdesirable that an outer side portion of the silicone gel that is opposedto the inner side portion of the silicone gel fully cure. This is sothat the outer side portion will have sufficient tackiness to adhere tothe absorbent core when pressed thereagainst and will thus enable thesilicone gel to finish curing while disposed on the absorbent coreitself.

The absorbent core is placed on the side of the facing layer that isopposite the side adjacent the carrier surface. Since the silicone gelis in a partially cured state, the silicone gel will cure and adhere tothe surface of the absorbent core. When the silicone gel has fullycured, the silicone layer is removed from the perforation device alongwith the absorbent core. Pressure may be exerted onto the absorbent coreand the facing layer to more fully adhere the facing layer to theabsorbent core.

The silicone layer may be removed from the perforation device prior tobe being applied to an absorbent core. In this instance, the siliconelayer may be peeled away from the perforation device when it is in apartially cured state, thus forming a discrete, partially cured siliconelayer that can be applied to a transfer film or substrate for futureapplication to an absorbent core or directly to a body member. Thetransfer film may be an air permeable paper or similar type of film orpaper that will easily permit the silicone layer to be applied andremoved therefrom when substantially or fully cured.

The perforation device may be modified in view of the descriptionprovided above. Specifically, the carrier surface of the perforationdevice may include a plurality of holes extending therethrough wherein aplurality of discrete perforation elements is slidably disposed throughthe plurality of holes. The method for using this perforation deviceincludes the steps of heating the planar surface and perforatingelements of the perforation device, and placing a layer of uncuredsilicone gel on the planar surface of the perforation device. Oncedisposed upon the planar surface, the perforation elements are driventhrough the silicone layer. After the silicone layer is at leastpartially cured, the perforation elements are withdrawn from thesilicone gel layer. An absorbent core may then be applied onto thesilicone layer as the silicone layer cures. Alternatively, the siliconelayer may be left to fully cure on the perforation device and thensubsequently removed, or the silicone layer may be removed prior tofully curing.

In another method for applying the facing layer to the absorbent core inthe present invention, a partially cured, silicone layer 12 is depositedonto a transfer film upon which apertures are formed in the siliconelayer 12 by rotating a mechanical roller 46 thereon. As exemplified inFIG. 21, the mechanical roller 46 has a patterned surface that issimilar in construction to the carrier surface 47 and the perforationelements 44 of the aforesaid perforation device 42 depicted in FIGS.19-20. In forming the apertures, perforation elements 44 of themechanical roller 46 are heated to about 100° C. or to the curingtemperature of the silicone layer. The mechanical roller 46 may eitherbe applied against the partially cured silicone layer after the siliconelayer 12 has been applied to the absorbent core 14 or may be appliedagainst the silicone layer while adhered to a transfer film prior to theapplication thereof to the absorbent core.

The mechanical roller may include the slidable perforating elements, asdescribed in reference to an embodiment of the perforating device andfunction generally in the same way.

In another method, uncured silicone gel may be extruded directly onto aheated mechanical roller, similar to the type described above, rotatingat a predetermined speed. A length of the absorbent core material issupported by a conveying surface and positioned below the mechanicalroller. As the mechanical roller rotates, the partially cured siliconegel is deposited onto the absorbent core material by the rotatingmechanical roller which applies at least a slight pressure on theabsorbent core. The mechanical roller is configured and arranged torotate at a sufficient speed so that the silicone gel will be nearly orfully cured as it leaves the carrier surface and is applied to theabsorbent core.

A silicone primer, such as a silicone primer manufactured by NuSilTechnology (Carpenteria, Calif.) under product designation CF6-135, maybe used to facilitate the bonding of the silicone layer to the absorbentcore.

In yet another method for applying a facing layer to an absorbent core,as exemplified in FIG. 22, a partially cured, non-perforated siliconelayer 12 may be applied to a transfer film 38. The film 38 carrying thesilicone layer 12 is then reversed in orientation so that the film 38defines an upper surface and the silicone layer 12 defines a lowersurface. The silicone layer 12 is then slowly positioned on an uppersurface of the absorbent core 14. After the silicone layer 12 is gentlypressed onto the absorbent core 14, a perforation device 42 carrying aplurality of perforating elements 44 having a similar construction tothe aforementioned perforation device 42 depicted in FIGS. 19 and 20 ispositioned over a lower surface of the absorbent core 14. Thisperforation device 42, however, is distinct from the perforation deviceof FIGS. 19 and 20 in that each of the perforating elements 44 includesa discrete air passageway and may generally be larger therefrom.

The perforating elements 44 are inserted into at least a portion of thethickness of the absorbent core 14 and air is blown through theprojection elements 44 towards respective portions of the silicone layer12. The air blown through the perforating elements 44 cures the siliconelayer 12 and further forms apertures through the silicone layer 12.After an adequate period of time and upon formation of the apertures,the device 42 carrying the needles 44 is withdrawn from the absorbentcore 14. The film 38 is subsequently removed from the silicone layer 12.A silicone primer, as described above, may be applied to the absorbentcore 14 to the application of the silicone layer 12 thereon to improvethe adherence of the silicone layer to the absorbent core.

In yet another method exemplified in FIGS. 23 and 24 for applying thefacing layer 12 to the absorbent core 14, a patterned negative surface48 is provided that bears the negative impression of the eventualsilicone layer 12. The patterned surface 48 includes a series of peaksand valleys 50, 52 that correspond to the eventual pattern of aperturesof the silicone layer 12. A partially-cured silicone gel 54 is appliedto the patterned surface 48 whereupon the silicone gel 54 rests in thevalleys 52 while at least a top portion of the peaks 50 extendtherethrough. The absorbent core 14 is subsequently positioned over thesilicone gel 54 with the top portion of the peaks 50 penetrating theabsorbent core 14. The silicone gel 54 is then bonded to the absorbentcore 14 and the patterned surface 48 is removed from the thus formedsilicone layer 12. Removal of the patterned surface 48 imparts apredetermined pattern of apertures on the silicone layer 12 thatcorrespond to the peaks 50 of the patterned surface 48.

In yet another method for applying a facing layer to an absorbent core,a silicone gel is mostly cured in a container. At a moment in which thesilicone gel has reached a suitably thick consistency, the silicone issprayed onto the absorbent core in a systematic manner so as to adherethereto. While the silicone is sprayed onto the absorbent core, aplurality of apertures is formed along the silicone layer. The sprayingof the silicone is conducted in a controlled manner that permits theholes to be formed in a non-random, predetermined pattern. The siliconelayer may be sprayed onto the absorbent core so as to include anundulating surface.

In each of the aforesaid methods for applying a facing layer onto anabsorbent core, it is essential that the silicone does not coat thewalls of the cells or pores of the absorbent core. The objective is notto occlude the cells or pores with silicone and provide uninhibitedtransport from the facing layer to the absorbent core. Furthermore, itis preferred that the holes formed through the silicone facing layer ofthe invention be arranged in a predetermined pattern so as to providegreater control of the fluid that passes through the silicone facinglayer when the dressing of the invention is applied to a wound site.

In any of the foregoing methods, the facing layer and the absorbent coreare adhered to each other substantially uniformly along their opposedareas. Furthermore, in each of the foregoing methods, the apertures ofthe facing layer may be formed either before or after the facing layeris applied to the absorbent core. The perforating elements or peaks mayor may not extend a distance into the absorbent core if the absorbentcore is applied to the facing layer while the facing layer is positionedon a perforation device. It will be understood, that it is preferredthat the facing layer be partially cured when applied to the absorbentcore so as to be sufficiently tacky to adhere to the absorbent core, yetsubstantially cured so that additional apertures are not formedtherethrough by capillary action of the cells or pores of the absorbentcore.

In a method exemplified in FIGS. 25-28, the preparation of the absorbentcore 14 of the dressing 20 of the invention may be conducted as follows.First, a plurality of projection elements 57 are heated to a suitabletemperature and are inserted into a surface of the absorbent core 14.The projection elements 57 are heated to a temperature in the range of200-300° C., preferably 255° C. The projection elements 57 extend intothe absorbent core 14 a distance less than its total thickness. Theprojection elements 57 are preferably arranged in a pattern bearing thenegative impression of the receptacles 18 of the absorbent core 14. Theprojection elements 57 are removed from the absorbent core 14 after aperiod of time, thereby forming the receptacles 18 in the absorbent core14.

The discrete portions of absorbent material 20 are deposited into thereceptacles 18 by positioning a silicone film 58 between aligned top andbottom plates 60, 62 having a plurality of holes 64 corresponding to theplurality of projection elements 57 used to form the receptacles 18. Apredetermined amount of the absorbent material 20 is deposited into eachof the holes of the top plate 60 and the projection elements 57 used toform the receptacles are inserted through the plurality of holes of thetop and bottom plates 60, 62, and the silicone film 58 so as to depositand compact the absorbent material 20 into each of the receptacles 18.

While the bulk amount of absorbent material in each receptacle may bevaried, it is preferred that the amount of absorbent material should notfill the entire receptacle since wetted absorbent material will swell.It will also be understood that it is important to the method that theportions of the absorbent material not be compacted in the receptaclesto the degree that migration of such absorbent material is obstructed.

It will be understood that the present invention is not limited to theaforementioned method for depositing the absorbent material in thereceptacles. Any method that may permit insertion and compaction ofdiscrete portions of absorbent material in the receptacles in acontrolled fashion may be employed while still remaining within thescope of the invention.

For example, a simple approach for depositing absorbent material in thereceptacles, in the event that superabsorbent granulates or powders areused, comprises the step of depositing the absorbent material into eachof the receptacles and then brushing, blowing or wiping off excessabsorbent material from the surface of the absorbent core. A vibrationtable or similar vibration mechanism may be used to urge the absorbentmaterial to settle in the receptacles.

In the aforementioned method, it will be understood that the facinglayer and the absorbent core are at least adhered and sealed to eachother at the border portions thereof. The importance of this is that thefacing layer must be secured to the absorbent core so that the discreteportions of absorbent material do not leak from the wound dressing.

A method for securing the backing layer 16 to the absorbent core 14 andformation of the compliant element 26 is preferably performed asillustrated in FIGS. 29-34. In a preferred method, a platen 66, as shownin FIG. 29, may be provided and configured with a profiled surface 70corresponding to the compliant element 26 and the central 22,intermediate 23 and border portions 24 of a dressing of an embodiment ofa wound dressing of the invention. The platen 66 is selectively incommunication with a vacuum configured to draw a vacuum along itsprofiled surface 70 and is heated to a temperature in the range of150-200° C., preferably 185° C. In a preferred embodiment, the platen 66includes a groove 68 that extends around the profiled surface 70 thatdefines the form of the compliant element 26. The platen 66 includes atleast one passageway 72 in communication with the groove 68 and avacuum. The platen 66 may also include a knife edge 74 that extendsaround the peripheral edge of the profiled surface 72 and a beveledportion 76 near the peripheral edge.

The platen 66 includes at least one recessed portion, such as recessedportions 78, 80, 82 and 84 shown in FIG. 29, that may be disposed abouta central portion of the platen 66. The recessed portions 78, 80, 82 and84 are preferably defined in a step-wise configuration with the centralrecessed portion 84 being relatively deeper than a first recessedportion 78. The at least one recessed portion is provided to reduce thepressure exerted at the localized region of the corresponding absorbentcore. This results, at least in part, in decreasing the level ofadherence of the backing layer at such localized region to the absorbentcore. It will be noted that the platen is not limited having recessedportions only in a central portion thereof and may be provided along anyportion of the platen where it is desired to have a localized region ofless adherence of a backing layer to an absorbent core.

The platen 66 may include a plurality of such passageways 72 that areutilized to communicate the vacuum with a backing layer 16. For example,the platen 66 may include 8 equally spaced passageways about the groove68 when an absorbent core has a generally rectangular shape. In thisexample, a passageway may be provided at a location corresponding tointermediate portion of the absorbent core and a passageway may beprovided between each corner. Moreover, the platen may include at leastone additional passageway 73 that is in communication with compressedair, and such at least one additional passageway may be disposed on theplaten corresponding to either the central or border portions.

It will be noted that the platen may be configured according to theshape of the eventual wound dressing and its individual features. Forexample, the platen may be arranged in a generally circular shape havinga groove that is generally circular.

As shown in FIG. 30, the backing layer 16 is placed over the absorbentcore 14, and then, as shown in FIG. 31, the platen 66 is positionedagainst the backing layer 16 and draws the backing layer 16 towards itsprofiled surface 70 by the vacuum. The platen 66 is continually drawntowards the absorbent core 14 while drawing the backing layer 16 againstits profiled surface 70. Of note is that a portion of the backing layer16 is preferably drawn into the groove 68, thereby forming at least aportion of the compliant element 26. In FIG. 31, the platen 66 is heatedat portions of the profiled surface 70 corresponding to the central,intermediate and border portions 22, 23, 24 of the eventual dressing.The surface of the groove 68 may or may not be heated.

In FIG. 32, the platen 66 positions the backing layer 16 against theabsorbent core 14. As can be seen in FIG. 33, the knife portion 74effectively cuts the absorbent core 14 and backing layer 16, and impartsthe beveled portion 28 of the border portion 24 to the dressing 10.Prior to withdrawing the platen 66 from the absorbent core 14, as shownin FIG. 33, the vacuum is removed from the profiled surface 72 and airprojected against the backing layer generally at the central portionthereof. As illustrated in FIG. 34, the platen 66 is subsequentlyremoved from the formed absorbent core 14 with the backing layer 16.

In another embodiment, the profiled surface of the platen may beconfigured so that a central portion thereof corresponding to thecentral portion of the dressing extends so that it imparts a thicknessto the absorbent core that is less than at the area corresponding to thecompliant layer and the border portion. This is so that the backinglayer will adhere more loosely to the absorbent core at the centralportion of the wound dressing. Due to the difference in thickness of theabsorbent core, the dressing will have the benefit that the discreteportions of absorbent material will cause the backing layer to detachfrom the absorbent core more effectively, and will further prevent thebacking layer from detaching from the border portion of the dressingbefore detaching at the central portion of the dressing.

It will be understood that the above described embodiments of theinvention may assume a variety of different shapes, sizes andconfigurations without departing from the scope of the presentinvention.

It will be understood that the above described embodiments of theinvention are illustrative in nature, and that modifications thereof mayoccur to those skilled in the art. Accordingly, this invention is not tobe regarded as limited to the embodiments disclosed herein, but is to belimited only as defined in the appended claims.

1. A wound dressing for covering a wound, comprising: a discrete skinadherent and resilient facing layer formed from a compound consisting ofa hydrophobic silicone gel and a skin treatment agent selected from thegroup consisting of aloe vera and petroleum jelly, the facing layerhaving a plurality of preformed and uniformly shaped apertures arrangedin a pattern; wherein the shape of the facing layer is defined byopposed, generally continuously planar outermost first and secondsurfaces, the apertures solely formed between the outermost first andsecond surfaces; and wherein one of the outermost first and secondsurfaces of the facing layer is in a partially cured state.
 2. The wounddressing according to claim 1, wherein the plurality of aperturesarranged in the pattern vary in number per unit area according to theirlocation relative to a center axis of the silicone gel layer.
 3. Thewound dressing according to claim 1, wherein the plurality of aperturesarranged in the pattern vary in size according to their locationrelative to a center axis of the silicone gel layer.
 4. The wounddressing according to claim 1, wherein the apertures are generallycircular.
 5. The wound dressing according to claim 1, wherein theapertures are generally equally spaced from one another.
 6. The wounddressing according to claim 1, wherein the pattern of the aperturescomprises alternating apertures of at least two different sizes.
 7. Thewound dressing according to claim 6, wherein the apertures have twodifferent sizes, the first size being larger than the second size andthe apertures of the first size being bordered by the apertures of thesecond size.
 8. The wound dressing according to claim 7, wherein theapertures of the second size are bordered by the apertures of the firstsize.
 9. The wound dressing according to claim 1, wherein the siliconegel layer has a progressive increase of tackiness extending from acentral portion to a border portion thereof.
 10. The wound dressingaccording to claim 1, wherein the silicone gel layer has regions ofvarying thickness.
 11. The wound dressing according to claim 1, whereinthe apertures of the facing layer have a diameter within the range of0.05 to 1.0 mm, and have a density of 50 to 350 apertures/cm².
 12. Awound dressing for covering a wound, comprising: a discrete skinadherent and resilient facing layer formed from a compound consisting ofa hydrophobic silicone gel, the facing layer having a plurality ofpreformed apertures arranged in a and non-apertured regions of thefacing layer consisting of the silicone gel; wherein the shape of thefacing layer is defined by opposed, generally continuously planaroutermost first and second surfaces, the apertures solely formed betweenthe outermost surfaces; and wherein one of the outermost first andsecond surfaces is in a partially cured state.